Axel Müller: One-dimensional hybrid nanoparticles based on cylindrical polymer brushes

Cylindrical (molecular) polymer brushes (CPBs) or ‘bottlebrush’ polymers, are versatile templates for the construction of nanorods, nanowires and nanotubes. CPBs possess side chains densely grafted from a linear backbone. Using the “grafting from” approach via ATRP or RAFT polymerization we have grown di- and triblock copolymers from a multi-initiator backbone, thus synthesizing well-defined core-shell and core-shell-corona CPBs with up to 4000 side chains.

We have used various functional core-shell CPB structures to generate hybrid nanowires of silica, semiconducting CdS and CdSe, superparamagnetic g ‑Fe₂O₃ and Fe₃O₄, catalytically active TiO₂ or ions of rare earth metals inside the core of CPBs. These have a number of applications, including bioimaging. Incorporating electron acceptors in the backbone and electron donors in the “antenna” side chains leads to a single-molecular light harvesting system with tunable energy transfer efficiency.

Water-soluble and biocompatible hybrid silica nanowires and nanotubes were successfully synthesized by sequentially grafting a silica precursor monomer, 3-(trimethoxysilyl)propyl acrylate (APTS) from a backbone. Hydrolytic crosslinking of the PAPTS block rendered a silica core with a water-soluble corona, which can host Au or Pd nanoparticles for catalysis. Uniform silica nanowires were achieved by pyrolysis. The length as well as the diameter of silica nanowires is well-defined. Growing triblock terpolymers with PAPTS middle block from the backbone finally resulted silica nanotubes.